Methods for producing hydrocarbon fluorides (fluorohydrocarbons) by reacting hydrogen-containing hydrocarbon halides (halohydrocarbons) with anhydrous hydrogen fluoride in a liquid phase using a stannic halide as a catalyst are described in U.S. Pat. Nos. 2,452,975 and 2,495,407 and Japanese Patent Publication No. 39086/72. In the method described in U.S. Pat. No. 2,452,975, a hydrogen-containing saturated hydrocarbon halide is reacted with anhydrous hydrogen fluoride in a liquid phase using stannic chloride as a catalyst; according to this patent, stannic chloride is milder in catalytic action than antimony halides which are common fluorination catalysts, and the formation of coke as a by-product is negligible when stannic chloride is used. In the method described in U.S. Pat. No. 2,495,407, a hydrogen-containing unsaturated hydrocarbon halide is reacted with anhydrous hydrogen fluoride using stannic chloride as a catalyst. In the method described in Japanese Patent Publication No. 39086/72, 1,1-difluoro-1-chloroethane is produced by reacting vinylidene chloride with hydrogen fluoride in the presence of stannic chloride; according to this patent, the formation of a by-product polymer is drastically reduced as compared with a method using antimony pentachloride as a catalyst, and since stannic chloride is less active to water than antimony pentachloride, the former can be reused as the catalyst if water content in the starting materials is low.
When a hydrogen-containing hydrocarbon halide such as 1,1,2-trichloroethane or 1,2-dichloro-1-fluoroethane is reacted with anhydrous hydrogen fluoride in a liquid phase using a stannic halide as a catalyst, higher boiling substances, oligomers or black precipitates are formed as by-products although their amounts are smaller than when an antimony halide is used as a catalyst. These by-products cause two major disadvantages: firstly, they reduce the selectivity for the end product; secondly, in industrial operations, equipment for removing or otherwise treating these by-products is necessary, rendering the overall manufacturing process complicated.
The terminology "higher boiling substances" means the compounds of fairly low molecular weights that are formed as a result of dimerization or trimerization of the hydrogen-containing hydrocarbon halide or its fluorine-substituted product. The "oligomers" are the products of further polymerization of such higher boiling substances. The "black precipitates" are those brown to black carbide-like substances which are not soluble either in the reaction solution formed upon completion of the fluorination or in water or acetone.
The present inventors found that the formation of higher boiling substances, oligomers or black precipitates occurred when a stannic halide was used as the sole catalyst for the fluorination of hydrogen-containing hydrocarbon halides. This phenomenon was particularly noticeable in the fluorination of 1,1,2-trichloroethane or 1,2-dichloro-1-fluoroethane. It is believed that the reason is as follows: when a hydrogen atom is present in the hydrocarbon halide, removal of hydrogen halides such as HCl or HF occurs during the reaction and the resulting dimerization or trimerization provides favorable conditions for the formation of higher boiling substances, oligomers or black precipitates.
The present inventors also found that when a hydrocarbon halide was reacted with anhydrous hydrogen fluoride in a liquid state using stannic chloride as a catalyst, the reaction mixture remained in a liquid form in the initial stage of reaction, but as the reaction proceeded, tin-derived tar started to form. The hydrocarbon halide and the anhydrous hydrogen fluoride were not completely miscible and formed two-liquid phases. The stannic chloride was liquid and was not soluble in the anhydrous hydrogen fluoride but soluble in the hydrocarbon halide and, as a result, the reaction solution was composed of two liquid phases. However, SnCl.sub.2 F.sub.2 and SnF.sub.4 which were fluorinated products of stannic chloride (SnCl.sub.4) were solid and were not soluble in either the anhydrous hydrogen fluoride or the hydrocarbon halide. As the reaction proceeds, the stannic chloride is also fluorinated. It is believed that the resulting fluorination products (e.g. SnCl.sub.2 F.sub.2 and SnF.sub.4) combine with a certain amount of the hydrocarbon halide to form a tar-like substance. This tin-derived tar clogs nozzles in the reactor or pipes and is a great obstacle to the purpose of carrying out the reaction in a continuous manner. Even if the catalyst is selected from stannic halides other than stannic chloride, stannic oxyhalides and organotin compounds, a similar tin-derived tar would be formed as the reaction proceeds.
It has heretofore been understood that oxygen-containing organic compounds and water are highly deleterious to the fluorination of hydrocarbons in the presence of metal halides, and these compounds and water are thoroughly removed from the starting material before reaction is started, as described in, for example, U.S. Pat. No. 2,005,708 and Yuki Fusso Kagaku (Chemistry of Organic Fluorine Compounds), Vol. I, p. 247, published by Gihodo Co. (1970). As a matter of fact, it was confirmed that fluorination catalyzed by antimony pentachloride or titanium tetrachloride was appreciably impeded by the addition of oxygen-containing organic compounds or water.